1. Field of the Invention
This invention relates to color video reproducing apparatus, such as a video tape recorder (VTR), and is particularly directed to a color video signal reproducing apparatus providing a time base corrected color video signal when operated in a normal-speed mode or in a non-normal speed mode, such as a stop-motion, slow-motion, fast-motion, or reverse mode.
2. Description of the Prior Art
Many color video signal reproducing apparatus are known which can accurately reproduce a recorded color video signal whether operated in a normal-speed reproducing mode or a non-normal-speed reproducing mode, such as stop motion, slow motion, fast motion, or reverse. One such apparatus, disclosed in U.S. Pat. No. 4,296,443, comprises a helical-scan VTR in which a pick-up head for scanning record tracks on magnetic tape is mounted for deflection in the direction transverse to the record tracks in each of which a field of video information is recorded.
In such a VTR, magnetic tape extends helically about at least a portion of the periphery of a guide drum, and is adapted to be moved or advanced in the longitudinal direction of the tape while at least a portion of the guide drum is rotated, and the magnetic pick-up head is supported on a bi-morph leaf or other deflectable support, which is in turn mounted on a rotating part of the guide drum. Thus, the magnetic head moves helically to scan each record track, and, owing to the deflectability of the bi-morph leaf, can follow the record tracks, even when the tape is advanced at a non-normal speed past the guide drum. Further, in the VTR disclosed in U.S. Pat. No. 4,296,443, an electrical drive signal for the bi-morph leaf is controlled to cause the head to jump to the next adjacent record track when the deflection of the bi-morph leaf approaches the physical limit possible therewith. By reason of such track jump, it is theoretically possible to effect correct slow-motion reproduction, fast-motion reproduction, still-picture reproduction, and even reverse-motion reproduction.
However, in non-normal reproduction modes, troubles arise by reason of time base variations of the reproduced signal. Such time base variations are caused mainly by the distance, measured in the direction along the record tracks, provided between the initial ends of the adjacent record tracks for achieving so-called H-alignment, and by the change occurring in the relative speed of the tape and magnetic head due to changeover of the speed of advancement of the tape. Other time base variations are caused, by example, by unavoidable fluctuations in the rotational speed of the magnetic head and in the speed of advancement of the tape past the guide drum. Of course, any fluctuations in the rotational speed of the magnetic head and the speed of advancement of the tape occurring during the recording operation also carry over into the reproduced signals to give rise to further time base variations.
The above-described time base variations can, for the most part, be corrected by means of existing time base correctors (TBCs), for example, as disclosed in U.S. Pat. Nos. 4,100,567 and 4,145,705.
Moreover, in low-speed reproduction, for example, reproduction at half of normal speed, the magnetic head is deflected to scan the same recorded track twice in succession. Also, in high-speed reproduction, such as reproduction at double normal tape speed, the magnetic head is deflected to scan only every other record track. Further, in still-frame or stop-motion reproduction, the same record track is scanned many times in succession. In any of such non-normal reproducing modes, time base correction is required to correct so-called jitter which occurs when an odd-field is substituted for an even video field, or vice versa.
In non-normal reproduction modes, the requirement to present a continuous chrominance component satisfying television system standards (i.e., color framing) gives rise to special problems. ln particular, in non-normal modes wherein record tracks are scanned repeatedly or are skipped, special measures must be taken to ensure correct color framing, that is, to ensure that the color subcarrier or the chrominance component of the video signal is provided in correct phase.
As is well known, in the NTSC, PAL, and SECAM color television signal systems, the phase of the color subcarrier shifts in successive video fields. This occurs because of the need to ensure a correct frequency-interleaving relationship between the luminance component and chrominance component of a composite color video signal. The color subcarrier frequency is selected to have a special non-integral phase relationship with respect to the horizontal synchronizing frequency. For example, in the NTSC color television signal system, the color subcarrier-frequency f.sub.sc is related to the horizontal frequency f.sub.h as ##EQU1## Consequently, four television fields must occur before the color subcarrier signal exactly repeats itself in phase with respect to the horizontal synchronizing signal. In other words, a cycle of four consecutive fields can be considered as a single color frame, and cycles of four consecutive fields are required to maintain the continuity of the color subcarrier.
If color framing is disregarded in the reproduction of a recorded color video signal, the resulting picture brightness can become irregular, and the picture quality can otherwise deteriorate. Because in helical-scan reproduction each recorded track of video tape constitutes a single video frame, this color framing must be carried out with respect to at least four consecutive tracks.
Other standard color television systems have similar requirements. For example, in the SECAM system, a color frame is constituted by four consecutive fields. In the PAL system, because of the line alternations of the B-Y color difference signal, a cycle of eight consecutive fields is required to constitute a single color frame.
Particular circuitry or forming the color frame lock signal is discussed in U.S. Pat. No. 4,115,800. For example, in a so-called C-format VTR, the color framing signal can be included in a control signal CTL, and a color frame servo operation can be performed on the basis of this signal CTL. Accordingly, the color frame lock signal is provided when the phase of the color subcarrier is locked according to a standard color frame cycle.
In order to achieve time base error correction of a reproduced composite video signal, it has been necessary to separate the reproduced video signal into its luminance and chrominance signal components, to correct any time base errors separately for each such component and then to recombine the corrected luminance and chrominance components. This has been required, at least in part, because correct color framing could not be easily carried out if the composite color video signal were time base corrected as an entity, i.e., as a composite signal. However, in digital time base corrector apparatus, such as those disclosed for example, in U.S. Pat. Nos. 4,100,567, and 4,145,705, wherein separate time base correctors are used for the luminance component and the chrominance component of a reproduced video signal, the phase of the subcarrier for the chrominance component can be adjusted for correct color framing when time base errors in the chrominance component are corrected.
While separate time base error correction of luminance and chrominance components has been adequate for non-normal reproduction, picture errors can occur during normal-speed reproduction. For example, if separate luminance and chrominance time base correction is carried out during normal-speed reproduction, the separate time base correctors impart different respective time delays to the luminance and chrominance components. Consequently, jitter, loss of color balance, and generally deteriorated picture quality can occur.